Xiaoyong Qin

The universal power and efficiency characteristics for irreversible reciprocating heat engine cycles

The performance of irreversible reciprocating heat engine cycles with heat transfer loss and friction-like term loss is analysed using finite-time thermodynamics. The universal relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, and the optimal relation between power output and the efficiency of the cycles are derived. Moreover, analysis and optimization of the model were carried out in order to investigate the effect of cycle processes on the performance of the cycle using numerical examples. The results obtained herein include the performance characteristics of irreversible reciprocating Diesel, Otto, Atkinson and Brayton cycles.

Optimization for a steam turbine stage efficiency using a genetic algorithm

Based on the genetic optimization theory, a design method for the flow path of an axial flow steam turbine stage is presented. In this method the maximum efficiency of the stage is taken as the objective, a series of functions are taken as constraints, and the optimal geometric and aerodynamic parameters are solved using the genetic algorithm process. The efficiency and constraints evaluation are performed using a program for the thermodynamic calculation of steam turbine stages in the design condition. The fitness of each individual is determined by the turbine efficiency and a penalty function containing the constraints. The proposed method is applied to the design of a real steam turbine stage. The results show that the new method successfully reveals the optimal geometric and aerodynamic parameters of the stage for maximum efficiency.

Thermodynamic modelling and performance of variable-temperature heat reservoir absorption refrigeration cycle

An irreversible variable-temperature heat reservoir four-temperature-level absorption refrigeration cycle model is established in this paper. The considered losses include heat resistances between heat reservoirs and working fluid, internal irreversibilities due to internal dissipation of the working fluid, and the heat leakages between the heat reservoirs and the surroundings. The general relationships between the cooling load and the COP are derived. Besides, the optimal performance characteristics between the cooling load and the COP are obtained using numerical examples. The effects of heat resistances, internal irreversibilities, heat leakages, and the thermal capacitance rates of heat reservoirs on the cycle performance are analysed.

Optimal Performance of an Endoreversible Four-Heat-Reservoir Absorption Heat-Transformer

Based on an endoreversible absorption heat-transformer cycle model operating between four temperature levels with linear (Newtonian) heat transfer law, the fundamental optimal relation between the specific heating load and the coefficient of performance, the optimal temperatures of the working substance, and the optimal heat transfer surface areas of the four heat exchangers are derived by using finite-time thermodynamics. Moreover, the effects of the cycle parameters on the cycle characteristic are studied by numerical examples. The results obtained herein can provide some guidance for the optimal design of absorption heat-transformers.

Performance of an endoreversible four-heat-reservoir absorption heat-transformer with a generalized heat transfer law

SYNOPSIS An endoreversible four-heat-reservoir absorption heat-transformer cycle model with a generalised heat transfer law Q α Δ(Tn) is established. The general relationship between coefficient of performance (COP) and heating load with Q α Δ(Tn) is deduced. The fundamental optimal relationship, the maximum heating load and the corresponding COP, the optimal temperatures of the working substance, as well as the optimal heat transfer surface area distributions with linear phenomenological heat transfer law, are derived. Moreover, the effects of the heat transfer law on the performance of an absorption heat-transformer are analysed, and the performance comparison is performed for the distribution of the total heat transfer surface area, optimised or not, by numerical example.

Compromise optimization between heating load and entropy production rate for endoreversible absorption heat pumps

SYNOPSIS On the basis of an endoreversible four-heat-reservoir absorption heat pump cycle model with linear (Newtonian) heat transfer law, an ecological optimisation criterion is proposed for the best mode of operation of the cycle, which consists of maximising a function representing the best compromise between the heating load and the entropy production rate. The optimal relation between the ecological criterion and the COP (coefficient of performance), and the maximum ecological criterion and the corresponding COP, heating load and entropy production rate are derived by using finite-time thermodynamics. Moreover, the ecological performance is compared with that for the heating load criterion by numerical example. The results reflect that ecological criterion is a factor which can have long-term significance for optimal design of absorption heat pumps.